The invention lies in the field of fuel injectors. The invention relates to a configuration and to a method for amplifying the pressure of fuel for a fuel injector.
Use of injection systems that operate with very high injection pressures for supplying fuel to internal combustion engines is increasing. Accumulator-type injection systems in which very high injection pressures are produced by pressure intensification have proven advantageous in this context, particularly for truck diesel engines. An example of a fuel injector with pressure amplification is illustrated in U.S. Pat. No. 5,682,858 to Chen et al.
In the prior art system, a pressure amplifier with a piston is movably disposed in the fuel injector. The piston divides the pressure amplifier into a control space on the low-pressure side and a working space on the high-pressure side. The working space on the high-pressure side of the pressure amplifier is connected to the fuel line in the fuel injector upstream of the actual injection nozzle. The control space on the low-pressure side is connected to an accumulator by an actuator-actuated servovalve formed in the fuel injector.
In the configuration, the servovalve is constructed such that, in the initial state, when the actuator is not actuated, the servovalve interrupts the flow connection between the accumulator and the control space of the pressure amplifier and keeps the control space unpressurized. In the operating state, the working space of the pressure amplifier fills with fuel through the fuel line.
The servovalve is then switched by activation of the actuator so that the flow connection between the accumulator and the control space in the pressure amplifier is opened and the piston in the pressure amplifier is subjected on the control-space side to the pressure in the accumulator. At the same time, the pressure established in the control space is amplified many times over by the piston in the pressure amplifier and transmitted to the fuel situated in the working space at the pressure amplifier.
The high-pressure fuel opens the injection nozzle in the fuel injector and the fuel is injected into a combustion chamber of the internal combustion engine. As soon as the activation of the actuator ends, the servovalve returns to its initial state. Consequently, the flow connection between the accumulator and the control space is, again, interrupted and the control space is returned to the unpressurized state. Then, the pressure on the fuel in the working space of the pressure amplifier falls abruptly and injection ends.
In the prior art accumulator-type injection system with pressure amplification, the quantity of fuel injected is determined by the time window of activation of the actuator and by the configuration of the injection nozzle, i.e., the quantity of fuel injected by the nozzle per unit time. Unavoidable manufacturing tolerances in the injection nozzle, therefore, inevitably detrimentally affects the fuel injector such that the quantity of fuel injected varies from fuel injector to fuel injector. Such variance can lead to nonuniform engine behavior, in particular, lack of engine smoothness, especially for multicylinder engines. Moreover, in the prior art configuration, the end of injection and, hence, the course of combustion in the combustion chamber depend on precise activation of the actuator and of the servovalve.
It is accordingly an object of the invention to provide a configuration and a method for amplifying the pressure of fuel for a fuel injector that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that refines existing configurations and methods for amplifying the pressure of fuel for a fuel injector to reduce the effect of manufacturing tolerances and switching operations upon the characteristics of injection into the internal combustion engine.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a configuration for amplifying the pressure of fuel for a fuel injector having an injection nozzle, including a pressure supply containing pressurized medium, a pressure line, a fuel line, a pressure amplifier having a low-pressure side, a high-pressure side, a control space on the low-pressure side, a working space on the high-pressure side, a moveable ram disposed between the control space and the working space, the control space connected to the pressure supply through the pressure line, and the working space connected to the fuel line upstream of an injection nozzle of a fuel injector, an actuator, a servovalve for changing between an actuated switched state and an unactuated initial state, the servovalve connected to and actuated by the actuator, disposed in the pressure line between the pressure supply and the control space, opening the pressure line in the unactuated initial state, and interrupting the pressure line and keeping unpressurized the control space in the actuated switched state when the servovalve is triggered by the actuator.
According to the invention, a servovalve is disposed between a control space of a pressure amplifier (the control space being on the low-pressure side) and an accumulator. The servovalve is actuated by an actuator configured such that, in the initial state, when the actuator is not activated, the servovalve keeps open the flow connection between the accumulator and the control space of the pressure amplifier and, hence, subjects a piston in the pressure amplifier to the pressure prevailing in the accumulator. Only when the actuator is activated is the flow connection between the accumulator and the control space interrupted and the control space kept unpressurized by the servovalve, with the result that the fuel is drawn in by the working space of the pressure amplifier.
In accordance with another feature of the invention, there is provided an outlet, and wherein the servovalve is a 3/2-way valve and connects the control space to the outlet in the actuated switched state.
In accordance with a further feature of the invention, the pressure line includes a restrictor upstream of the servovalve.
With the objects of the invention in view, there is also provided a method for amplifying the pressure of fuel for a fuel injector having an injection nozzle, including the steps of connecting a pressure supply containing a pressurized medium to a pressure amplifier having a low-pressure side, a high-pressure side, a control space on the low-pressure side, a working space on the high-pressure side, and a ram movably disposed between the control space and the working space, providing a pressure line and connecting the pressure supply to the control space with the pressure line, providing a fuel line for guiding fuel, connecting the working space to an upstream side of an injection nozzle of a fuel injector with the fuel line for passing fuel to the working space, providing a servovalve, an actuator, and a pressure line, and placing the servovalve in the pressure line between the pressure supply and the control space of the pressure amplifier, connecting the actuator to the servovalve for actuating the servovalve, opening the pressure line with the servovalve when the actuator is unactuated, and interrupting the pressure line and keeping unpressurized the control space with the servovalve when the actuator is actuated and actuates the servovalve.
In accordance with an added mode of the invention, the beginning of injection is set through the injection nozzle to occur when activation of the actuator ends, causing automatic return of the servovalve to an open position of the pressure line.
In accordance with an additional mode of the invention, the open position of the pressure line is held with the servovalve and the actuator at least until the prevailing pressure of the medium in the control space and acting on the ram has forced fuel completely out of the working space in the pressure amplifier.
In accordance with a concomitant feature of the invention, the quantity of fuel injected is determined by the injection nozzle by the volume of the working space in the pressure amplifier.
The end of actuator activation fixes the beginning of injection through an injection nozzle. The servovalve returns automatically to its initial state and the flow connection between the accumulator and the control space of the pressure amplifier opens again. The pressure established in the control space is amplified many times over by a piston in the pressure amplifier and is transmitted to the fuel in the working space of the pressure amplifier. The fuel subjected to high pressure in the working space causes the injection nozzle to open and fuel to be injected into a combustion chamber of the internal combustion engine. The injection process ends automatically as soon as all the fuel held in the working space of the pressure amplifier has been injected.
According to the invention, the fuel drawn into the working space solely determines the quantity injected. Manufacturing tolerances of the injection nozzle, thus, have no effect on the metered injection quantity. Moreover, the injection process is ended automatically as soon as all the fuel drawn into the working space has been injected. The completion of fuel transfer ensures a sharply defined end to injection and, hence, improved combustion values.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a configuration and method for amplifying the pressure of fuel for a fuel injector, it is nevertheless not intended to be limited to the details shown, because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.